Multi-vector implantable cardioverter-defibrillator systems and methods with improved electrical symmetry

ABSTRACT

Implantable cardioverter device (ICD) systems capable of delivering a multi-vector defibrillation shock, and methods for use therewith, are described herein. Such an ICD system can include a defibrillation charge capacitor, a charge circuit, first, second, and third electrodes, switches, a controller, and first, second and third filters. The defibrillation charge capacitor is coupled between a first voltage rail and a second voltage rail. The first filter is coupled between the first and second electrodes, and the second filter is coupled between the second and third electrodes, so that the first and second filters can shunt EMI signals. The third filter is coupled between the first and third electrodes and configured to provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock. Such filters, which can be implemented using capacitors, can be used to make the ICD system MRI compatible.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Patent Application No. 62/824,242, filed Mar. 26, 2019, which is incorporated herein by reference in its entirety.

FIELD OF TECHNOLOGY

This disclosure is directed to medical devices and methods for use therewith. More specifically, embodiments disclosed herein relate to multi-vector implantable cardioverter-defibrillator (ICD) systems and methods that improve electrical symmetry. Such improved electrical symmetry can provide for compatibility with magnetic resonance imaging (MRI) systems, or more generally, provide protection from electromagnetic interference (EMI).

BACKGROUND

An implantable cardioverter-defibrillator (ICD) is an implantable medical device equipped to detect and treat atrial fibrillation (AF) and/or ventricular fibrillation (VF) and deliver electrical shocks to terminate VF. Typically, the metal case or housing (or “can”) of the ICD is used as a shocking electrode along with a coil electrode implanted on or in the heart of the patient. In such an example, the case electrode and the coil electrode collectively define a vector that is used to deliver a defibrillation shock, which vector can also be referred to as a defibrillation vector. The case electrode can also be referred to as the “can” electrode or housing electrode, but will be primarily referred to herein as the case electrode. Exemplary coil electrodes that can be used to deliver a defibrillation shock, along with the case electrode, include a right ventricular (RV) coil electrode, or a superior vena cava (SVC) coil electrode, which can also be referred to more succinctly as an RV electrode and an SVC electrode, respectively. Where only two electrodes (e.g., a case electrode and an RV electrode) are used to deliver a defibrillation shock, there is only a single defibrillation vector, and thus, the delivered stimulation can be referred to more specifically as a single-vector defibrillation shock.

While single-vector defibrillation shocks are typically successful in terminating VF, there are certain times and/or patient populations for which it may be preferred to deliver a multi-vector defibrillation shock. For example, if a single-vector defibrillation shock is unsuccessful at terminating VF, then a multi-vector defibrillation shock may be tried to increase a probability of terminating the VF on the next shock. As implied by its name, multiple defibrillation vectors are used to deliver a multi-vector defibrillation shock, requiring the use of at least three electrodes to deliver the multi-vector defibrillation shock. For example, a case electrode, RV electrode, and SVC electrode may all be used to deliver a multi-vector defibrillation shock.

Recently there has been a desire to design and manufacture ICDs such that they are compatible with magnetic resonance imaging (MRI) systems, to thereby enable patients having ICDs to be imaged using MRI systems. However, the inclusion of MRI compatibility into ICDs may cause to certain technical issues that should be overcome, some of which are discussed below. More generally, there is a desire to provide protection from electromagnetic interference (EMI), wherein the EMI may be caused by an MRI system and/or some other source of EMI.

SUMMARY OF THE DISCLOSURE

A summary of several sample aspects of the disclosure follows. It should be appreciated that this summary is provided for the convenience of the reader and does not wholly define the breadth of the disclosure. For convenience, one or more aspects or embodiments of the disclosure may be referred to herein simply as “some aspects” or “certain embodiments.”

Certain embodiments of the present technology are related to implantable cardioverter device (ICD) systems, and methods for use therewith. Such an ICD system can be configured to be implanted within a patient and capable of delivering a multi-vector defibrillation shock. In accordance with certain embodiments, the ICD system includes at least one defibrillation charge capacitor, a charge circuit, first, second, and third electrodes, a plurality of switches, a controller, and first, second and third filters. The at least one defibrillation charge capacitor is coupled between a first voltage rail and a second voltage rail, wherein the second voltage rail acts as a return path, relative to the first voltage rail, for defibrillation shocks delivered to patient tissue. The charge circuit is configured to selectively cause a high voltage potential to be stored on the at least one defibrillation charge capacitor. The first, second, and third electrodes can be used to selectively deliver at least a portion of the high voltage potential, stored on the at least one defibrillation charge capacitor, to patient tissue that is in contact with at least one of the first, second, and third electrodes. The controller is configured to control the plurality of switches to selectively connect a first subset of the first, second, and third electrodes to the first voltage rail, and selectively connect a second subset of the first, second, and third electrodes to the second voltage rail, such that there is no overlap between electrodes within the first and second subsets. The first filter is coupled between the first and second electrodes, and the second filter is coupled between the second and third electrodes, so that the first and second filters can shunt electromagnetic interference (EMI) signals and/or other unwanted signals. The third filter is coupled between the first and third electrodes and configured to provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock.

In order to deliver a biphasic multi-vector defibrillation shock, the controller can control the plurality of switches to: connect the first subset of the first, second, and third electrodes to the first voltage rail, and connect the second subset of the first, second, and third electrodes to the second voltage rail, for a first period of time during which the high voltage potential is being discharged; and thereafter connect the first subset of the first, second, and third electrodes to the second voltage rail, and connect the second subset of the first, second, and third electrodes to the first voltage rail, for a second period of time during which the high voltage potential is being discharged (or vice versa).

In accordance with certain embodiments, the first electrode is a right ventricular (RV) electrode, the second electrode is a case electrode, and the third electrode is a superior vena cava (SVC) electrode. Other variations are also possible and within the scope of the embodiments described herein.

In accordance with certain embodiments, the switches are controlled to selectively connect: two of the first, second, and third electrodes to the first voltage rail and a remaining one of the first, second, and third electrodes to the second voltage rail. Alternatively, the switches can be controlled to selectively connect, one of the first, second, and third electrodes to the first voltage rail and a remaining two of the first, second, and third electrodes to the second voltage rail.

In accordance with certain embodiments, the first filter, which is coupled between the first and second electrodes, comprises a first capacitor having a first terminal coupled to the first electrode and a second terminal coupled to the second electrode, the first capacitor having a first capacitance. The second filter, which is coupled between the second and third electrodes, comprises a second capacitor having a first terminal coupled to the second electrode and a second terminal coupled to the third electrode, the second capacitor having a second capacitance. The third filter, which is coupled between the first and third electrodes, comprises a third capacitor having a first terminal coupled to the first electrode and a second terminal coupled to the third electrode, the third capacitor having a third capacitance. In accordance with certain embodiments, the first, second and third capacitances are substantially equal to one another to thereby provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock.

In accordance with certain embodiments, one or more of the first, second, and third capacitors comprise feedthrough capacitor(s) that is/are located within a header of the ICD system.

In accordance with certain embodiments, one or more of the first, second, and third capacitors is/are located on or within a substrate that is within a housing of the ICD system.

In accordance with certain embodiments, the first, second, and third electrodes, the first and second filters, and the plurality of switches, are collectively configured to provide a plurality of H-bridge circuits, wherein inclusion of the third filter causes the H-bridge circuits to be electrically symmetrical, and wherein at least one of the H-bridge circuits would be asymmetrical if the third filter were not present.

In accordance with certain embodiments, the switches are silicon-controlled rectifiers.

In accordance with certain embodiments, the filters provide compatibility with magnetic resonance imaging (MRI) systems, and more generally, provide protection from electromagnetic interference (EMI).

Certain embodiments of the present technology are related to methods for use with an ICD system that includes at least one defibrillation charge capacitor coupled between first and second voltage rails, and also includes first, second, and third electrodes. Such a method can include providing a first filter coupled between the first and second electrodes, a second filter coupled between the second and third electrodes, and a third filter coupled between the first and third electrodes. The method can also include causing a high voltage potential to be stored on the at least one defibrillation charge capacitor coupled between the first voltage rail and the second voltage rail. The method can further include connecting a first subset of the first, second, and third electrodes to the first voltage rail, and a second subset of the first, second, and third electrodes to the second voltage rail, the first and second subsets differing from one another. Further, the method can include discharging at least a portion of the high voltage potential stored on the at least one defibrillation charge capacitor, while the first subset of the first, second, and third electrodes are connected to the first voltage rail, and the second subset of the first, second, and third electrodes are connected to the second voltage rail.

In order to deliver a biphasic defibrillation shock, the method can further include (after discharging a portion of the high voltage potential stored on the at least one defibrillation charge capacitor), connecting the first subset of the first, second, and third electrodes to the second voltage rail, and the second subset of the first, second, and third electrodes to the first voltage rail, and discharging a further portion of the high voltage potential stored on the at least one defibrillation charge capacitor (while the first subset of the first, second, and third electrodes are connected to the second voltage rail, and the second subset of the first, second, and third electrodes are connected to the first voltage rail).

The method can further include shunting electromagnetic interference (EMI) signals using the first filter coupled between the first and second electrodes, the second filter coupled between the second and third electrodes, and the third filter coupled between the first and third electrodes.

In the above summarized method, the first filter coupled between the first and second electrodes, the second filter coupled between the second and third electrodes, and the third filter coupled between the first and third electrodes, provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock.

In accordance with certain implementations of the above summarize method, the first filter, which is coupled between the first and second electrodes, comprises a first capacitor having a first terminal coupled to the first electrode and a second terminal coupled to the second electrode, the first capacitor having a first capacitance. The second filter, which is coupled between the second and third electrodes, comprises a second capacitor having a first terminal coupled to the second electrode and a second terminal coupled to the third electrode, the second capacitor having a second capacitance. The third filter, which is coupled between the first and third electrodes, comprises a third capacitor having a first terminal coupled to the first electrode and a second terminal coupled to the third electrode, the third capacitor having a third capacitance. In accordance with certain embodiments, the first, second and third capacitances are substantially equal to one another to thereby provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock.

This summary is not intended to be a complete description of, or limit the scope of, the present technology. Alternative and additional features, aspects, and objects of the present technology can be obtained from a review of the specification, the figures, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the present technology are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present technology will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the present technology are utilized, and the accompanying drawings of which:

FIG. 1A illustrates an exemplary ICD system.

FIGS. 1B, 1C, and 1D are used to describe how the ICD system introduced in FIG. 1A includes three H-bridge circuits.

FIG. 1E illustrates how the ICD system introduced in FIG. 1A can be used to deliver a multi-vector defibrillation shock, and the potential problems associated therewith.

FIG. 1F illustrates exemplary voltage potential waveforms that can be produced between various nodes of the ICD system described with reference to FIGS. 1A through 1E.

FIG. 2A illustrates an exemplary ICD system according to an embodiment of the present technology.

FIG. 2B is used to describe how the ICD system, introduced in FIG. 2A, provides electrical symmetry and avoids certain problems that can occur with the ICD system described with reference to FIGS. 1A through 1F.

FIG. 2C includes an example case-to-HVN voltage potential waveform and an example SVC-to-HVN voltage potential waveform.

FIG. 3 is a high level flow diagram that is used to summarize methods according to various embodiments of the present technology.

FIG. 4A illustrates an exemplary cardiac stimulation device within which embodiments of the present technology can be implemented.

FIG. 4B is a simplified block diagram of internal components of the cardiac stimulation device introduced in FIG. 4A.

DETAILED DESCRIPTION

As noted above, there has been a desire to design and manufacture ICDs such that they are compatible with MRI systems, to thereby enable patients having ICDs to be imaged using MRI systems. However, the inclusion of MRI compatibility into ICDs may cause certain technical issues that should be overcome, some of which are discussed below.

For example, with the inclusion of MRI compatibility into ICDs, one problem to solve is how to achieve MRI compatibility while maintaining the ability to provide two or more high voltage therapy vectors. While there exist several techniques for providing adequate MRI filtering, involving using shunting and/or filtering circuits to shunt and/or filter out MRI frequency electrical aggressor signals, these shunting/filtering circuits can imbalance the ICD against a multi-vector high voltage therapy return path, leading to incompatible/marginal MRI compatibility performance, reduced/improper high voltage therapy functionality, reduced circuit efficiency and/or other electrical compatibility/therapy delivery issues that should be solved.

When an implanted ICD is exposed to electromagnetic interference (EMI) signals from an MRI system, MRI return paths originate from one or more patient leads containing electrical contacts that are returned/shunted through the case electrode of the ICD. Within the ICD, High Voltage (HV) return paths typically have different ‘high side’ to ‘low side’ electrical circuit loops, sending energy through the body with the intent of stimulating tissue. These circuit loops have electrodes positioned based upon physiology to stimulate specific muscle/tissue, thereby creating the need for different return paths in comparison to MRI return paths. A circuit containing both high side and low side electrical loops should have a robust solution in place to adequately perform for both uses—a circuit not optimized for one or the other, but for both uses.

To provide for MRI compatibility, or more generally EMI compatibility, an ICD may include capacitors coupled between electrodes. Where such capacitors are included within the header of an ICD, such capacitors are often referred to as feedthrough (FT) capacitors or feedthrough filter capacitors. Such capacitors that are used to provide for EMI compatibility can alternatively be located within the housing (i.e., case or “can”) of the ICD, e.g., within or on a substrate, such as a printed circuit board (PCB), of the ICD.

Certain embodiments of the present technology described herein provide a scheme for balancing (creating symmetrical) MRI filters with respect to the high voltage return path loops, ensuring both MRI compatibility and multi-vector high voltage therapy performance. More specifically, certain embodiments of the present technology relate to circuitry that provides a balanced H-bridge between two or more vectors with appropriate MRI filtering in-place within the circuit. In accordance with certain embodiments, the balanced H-bridge is designed such that the positive node(s) of the high voltage electrode is/are symmetrically equivalent across the negative nodes(s) of the return path.

FIG. 1A illustrates an exemplary ICD system 102, which can include both an ICD housing or “can” as well as one or more leads connected thereto. The ICD system 102, which can also be referred to more succinctly as an ICD 102, is shown as including a battery 104, a charge circuit 108, a diode 110, a defibrillation charge capacitor C_(charge), a plurality of electrodes 116 a, 116 b, and 116 c, a plurality of switches Sw1-Sw6, and feedthrough capacitor C_(FT1) and C_(FT2). The electrodes 116 a, 116 b, and 116 c can be referred to collectively as the electrodes 116, or individually as an electrode 116. While only three electrodes 116 are shown in FIG. 1A, the ICD 102 can include more than three electrodes 116. The resistor symbols shown in FIG. 1A, which are labeled R1, R2, and R1, are shown in dotted lines in a star-configuration and are representative of the resistances associated with the patient tissue that is in contact with the electrodes 116. The ICD 102 is also shown as including a controller 120. The controller 120 can be used to control the switches Sw1-Sw6. The same controller, or a different controller (not shown), can be used to control the charge circuit 108. The switches Sw1-Sw6 can be implemented, e.g., using a silicon-controlled rectifiers (SCRs), but are not limited thereto. The feedthrough capacitors C_(FT1) and C_(FT2) can beneficially shunt and/or filter out MRI frequency electrical aggressor signals and/or other types of EMI when the ICD 102 is used to deliver a single-vector defibrillation shock.

The charge circuit 108, which is coupled to the battery 104, is used to store energy received from the battery 104 on the defibrillation charge capacitor C_(charge). The charge circuit 108 can be used, e.g., to step-up the battery voltage to a desired high voltage for use in delivering a defibrillation shock. For example, if the battery voltage is 3.3V, and the desired voltage of the stimulation pulse is 900V, then the charge circuit 108 can be used to step-up the voltage from 3.3V to 900V. The charge circuit 108 can be implemented, e.g., as a charge pump, a boost converter, or some other type of DC-DC converter, but is not limited thereto. The diode 110 is used to allow current to flow from the charge circuit to the defibrillation charge capacitor C_(charge), but not in the reverse direction.

The defibrillation charge capacitor C_(charge) is shown as being coupled between a high voltage rail 112 and a low voltage rail 114, which can be referred to more generally as a first voltage rail 112 and a second voltage rail 114. The high voltage rail 112 is labeled HVP, which stands for High Voltage Positive, and the low voltage rail 114 is labeled HVN, which stands for High Voltage Negative. Nevertheless, it is noted that the low voltage rail 114 can be at a virtual ground level, and thus, need not be negative. Rather, it is presumed that the low voltage rail 114 is at a significantly lower voltage level than the high voltage rail 112. In accordance with the embodiment described herein, the low voltage rail 114 acts as a return path, relative to the high voltage rail 112, for defibrillation shocks delivered to patient tissue. The battery 104 is shown as being coupled between ground and the charge circuit 108. The ground may be the same as the low voltage rail 114, however that need not be the case. While not specifically shown in FIG. 1A, and the other similar FIGS. (e.g., FIGS. 1B-1E), a sense resistor can be coupled between the lower switches (Sw4, Sw5, and Sw6) and the low voltage rail 114, to enable a current passing through the circuitry to be measured. Such a sense resistor can have a relatively low resistance, e.g., 50 milliohms (mΩ), but is not limited thereto. In certain embodiments, such a current can be measured by determining a voltage drop across the sense resistor (which has a known resistance, e.g., 50 mΩ), and using ohms law to determine the current based on the voltage drop, i.e., using the equation I=V/R, where I is the current, V is the measured voltage drop, and R is the known resistance of the sense resistor.

While only one defibrillation charge capacitor C_(charge) is shown in FIG. 1A, it is possible that the ICD includes more than one defibrillation charge capacitor C_(charge) to store a high voltage potential used for delivering a defibrillation shock. Such multiple defibrillation charge capacitors may be coupled in series and/or parallel to provide a desired capacitance, e.g., 110 microfarads (uF). For example, a pair of 220 uF defibrillation charge capacitors can be coupled in series to provide a capacitance of 110 uF. Accordingly, it can be more generally said that the charge circuit 108 is configured to selectively cause a high voltage potential to be stored on at least one defibrillation charge capacitor.

An H-bridge is an electronic circuit that switches the polarity of a voltage applied to a load. The exemplary ICD system 102 introduced in FIG. 1A includes three H-bridges, as shown in FIGS. 1B, 1C, and 1D. More specifically, a first H-bridge is shown in FIG. 1B, a second H-bridge is shown in FIG. 1C, and a third H-bridge is shown in FIG. 1D.

The electrodes 116 of the ICD system 102 are used to selectively deliver a high voltage potential (or at least a portion thereof), stored on the defibrillation charge capacitor C_(charge) (or stored on multiple defibrillation charge capacitors), to patient tissue that is in contact with at least two of the electrodes 116. The switches Sw1 through Sw6 are used to selectively couple any individual one of the electrodes 116 to either the high voltage rail 112 or the low voltage rail 114. If only one of the electrodes 116 is coupled to the high voltage rail 112, while only one of the other electrodes 116 is coupled to the low voltage rail 114 (with the remaining electrode(s) not coupled to either one of the voltage rails), then a single-vector defibrillation shock can be delivered to patient tissue. However, if more than one of the electrodes 116 is coupled to the same voltage rail, while another one (or more) of the electrodes 116 is (/are) coupled to the other voltage rail, then a multi-vector defibrillation shock can be delivered to patient tissue. For example, a multi-vector defibrillation shock can be delivered to patient tissue by coupling the electrode 116 a (e.g., the RV electrode) to the high voltage rail 112, and coupling the electrodes 116 b and 116 c (e.g., the case and SVC electrodes) to the low voltage rail. More specifically, the controller 120 can close the switches Sw1, Sw5, and Sw6 (and open, or leave open the remaining switches Sw2, S3 and Sw4) to thereby couple the electrode 116 a to the high voltage rail 112, and couple the electrodes 116 b and 116 c to the low voltage rail 114, as shown in FIG. 1E. This would provide for a first defibrillation vector between the electrodes 116 a and 116 b, and a second defibrillation vector between the electrodes 116 a and 116 c. If there is a desire to deliver a biphasic multi-vector defibrillation shock, as is often desired, then: a first portion of the multi-vector defibrillation shock could be delivered by closing the switches Sw1, Sw5, and Sw6 (and opening, or leaving open the remaining switches Sw2, S3 and Sw4) to thereby couple the electrode 116 a to the high voltage rail 112, and couple the electrodes 116 b and 116 c to the low voltage rail 114, as shown in FIG. 1E; and a second portion of the multi-vector defibrillation shock could be delivered by closing the switches Sw2, Sw3, and Sw4 and opening the switches Sw2, S3 and Sw4 to thereby couple the electrode 116 a to the low voltage rail 112, and couple the electrodes 116 b and 116 c to the high voltage rail 112. The phrases closing a switch and turning on a switch are used interchangeably herein, and the phrases opening a switch and turning off a switch are used interchangeably herein.

Still referring to FIG. 1E, initially when the switches Sw1, Sw5, and Sw6 are closed (and the switches Sw2, S3 and Sw4 are opened, or left open), the feedthrough capacitors C_(FT1) and C_(FT2) would effectively function as shunts or short circuits to high frequency components of current that passes through the switch Sw1. This would result in the current paths 122, 124, and 126 shown in FIG. 1E. More specifically, the current 122 would travel through the switch Sw1 and the feedthrough capacitor C_(FT1), and then be split between the current paths 124 and 126, as shown in FIG. 1E. As can be appreciated from FIG. 1E, the current 124 only travels through the feedthrough capacitor C_(FT1), yet the current 126 travels through both of the feedthrough capacitors C_(FT1) and C_(FT2). This results in the voltage potential waveform between the electrode 116 b and the low voltage node (referred to as the case-to-HVN voltage) being different than the voltage potential waveform between the electrode 116 c and the low voltage node (referred to as the SVC-to-HVN voltage). Examples of such voltage potential waveforms are shown in FIG. 1F. More specifically, referring to FIG. 1F, the waveform 140 shows an example of the case-to-HVN voltage, and the waveform 142 shows an example of the SVC-to-HVN voltage.

As can be appreciated from the waveform 142 in FIG. 1F, and the circuit shown in FIG. 1E, there will be a point in time during which a lower terminal of the switch Sw3 (e.g., a silicon-controlled rectifier), which is electrically coupled to the electrode 116 c (the SVC), is strongly pulled negative. This can have the undesirable consequence of causing the switch Sw3 to be inadvertently closed (also referred to as turned on), which effectively would cause the high voltage rail 112 (also referred to as HVP) to be coupled directly to the low voltage rail (HVN). This could lead to further undesirable consequences.

If current were to travel directly from the high voltage rail 112 to the low voltage rail 114, then substantially no current would travel through the patient tissue (represented by the resistors R1, R2, and R3), and thus, a needed defibration shock would not be delivered to the patient tissue. While not specifically shown in FIG. 1E (and the other similar FIGS.), the ICD system 102 can also include circuitry that monitors the current through a sense resistor (discussed above), such that if the current exceeds a specified threshold, the ICD system 102 would be shut down to avoid damage to the ICD system 102. This also could have the effect of preventing a needed defibrillation shock from being delivered to the patient tissue. Further, if the ICD system 102 failed to be shut down, the ICD system 102 could be irreparably damaged, again preventing a needed defibrillation shock from being delivered to the patient tissue. These aforementioned problems result from there being an imbalance in an H-bridge circuit, or stated another way, from their being a non-symmetric H-bridge circuit. Embodiments of the present technology, described below initial with reference to FIG. 2A, overcome the aforementioned problems by providing a balanced H-bridge circuit, which can also be referred to as a symmetric H-bridge circuit, and more generally can be referred to as an electrically symmetrical circuit.

Referring to FIG. 2A, an ICD system 202 according to an embodiment of the present technology is shown therein. Components of the ICD system 202 that are the same as the ICD system 102 (initially discussed above with reference to FIG. 1A) are labeled the same and need not be described in detail again. A comparison between FIG. 2A and FIG. 1A shows that the ICD system 202 includes a further feedthrough capacitors C_(FT3) coupled between the electrodes 116 a and 116 c, which feedthrough capacitors C_(FT3) was not included in the ICD system 102. As can be appreciated from FIG. 2B, this additional feedthrough capacitor C_(FT3) provides for a balanced H-bridge circuit, which can also be referred to as a symmetric H-bridge circuit, and can more generally be referred to as an electrically symmetrical circuit. As noted above, the feedthrough capacitors C_(FT1) and C_(FT2) can beneficially shunt and/or filter out MRI frequency electrical aggressor signals and/or other types of EMI when an ICD (e.g., 102 or 202) is used to deliver a single-vector defibrillation shock. The addition of the feedthrough capacitor C_(FT3) beneficially improves the shunting and filtering of MRI frequency electrical aggressor signals and/or other types of EMI when the ICD 202 is used to deliver a multi-vector defibrillation shock.

Referring to FIG. 2B, as was also the case in FIG. 1E, in FIG. 2B the switches Sw1, Sw5, and Sw6 are closed, and the switches Sw2, S3 and Sw4 or open, to thereby couple the electrode 116 a to the high voltage rail 112, and couple the electrodes 116 b and 116 c to the low voltage rail 114. As was also the case in FIG. 1E, this would provide for a first defibrillation vector between the electrodes 116 a and 116 b, and a second defibrillation vector between the electrodes 116 a and 116 c.

Still referring to FIG. 2B, initially when the switches Sw1, Sw5, and Sw6 are closed, the feedthrough capacitors C_(FT1), C_(FT2) and C_(FT3) would effectively function as shunts or short circuits to high frequency components of current that passes through the switch Sw1. This would result in the current paths 232 and 234 shown in FIG. 2B. More specifically, the current 232 would travel through the switch Sw1 and the feedthrough capacitor C_(FT1) before reaching the electrode 116 b, and the current 242 would travel through the switch Sw1 and the feedthrough capacitor C_(FT3) before reaching the electrode 116 c. If the capacitive values of the feedthrough capacitors C_(FT1), C_(FT2) and C_(FT3) are substantially the same (i.e., within 10 percent of one another), then this would result in the voltage potential waveform between the electrode 116 b and the low voltage node (referred to as the case-to-HVN voltage) being substantially the same as the voltage potential waveform between the electrode 116 c and the low voltage node (referred to as the SVC-to-HVN voltage). Examples of such voltage potential waveforms are shown in FIG. 2C. More specifically, referring to FIG. 2C, the waveform 240 shows the case-to-HVN voltage, and the waveform 242 shows the SVC-to-HVN voltage.

The waveforms 240 and 242 in FIG. 2C are substantially similar. In comparison to what occurs with the waveforms discussed above with reference to FIG. 1F, with the waveforms 240 and 242, there will not be a point in time during which a lower terminal of the switch Sw3, which is electrically coupled to the electrode 116 c (the SVC), is strongly pulled negative. Thus, the undesirable consequences that would result if the switch Sw3 is inadvertently closed (also referred to as turned on) are advantageously avoided.

The added feedthrough capacitor C_(FT3) will also provide for a symmetric H-bridge circuit for other multi-vector defibrillation configurations, besides the specific one discussed with reference to FIG. 2B.

The feedthrough capacitors C_(FT1), C_(FT2) and C_(FT3) can be included within the header of an ICD to provide for EMI compatibility. In alternatively embodiments, one or more of (and potentially all of) these capacitors need not be “feedthrough” capacitors, but rather, can be located within the housing (i.e., case or “can”) of the ICD, e.g., within or on a substrate, such as a printed circuit board (PCB), of the ICD.

The capacitor C_(FT1) is an example of a filter coupled between the electrodes 116 a and 116 b, the capacitor C_(FT2) is an example of a filter coupled between the electrodes 116 b and 116 c, and the capacitor C_(FT3) is an example of a filter coupled between the electrodes 116 a and 116 c. To provide for the desired electrical symmetry, the values of the feedthrough capacitors C_(FT1), C_(FT2) and C_(FT3) should be substantially the same (i.e., within 10 percent of one another),

A purpose of these capacitors, or more generally filters, is to shunt EMI signals, e.g., to provide for MRI compatibility, but not limited thereto. In alternative embodiments, alternative types of filters, such as RC filters, can be used to shunt EMI signals. In other words, embodiments of the present technology are not limited to the use of solely capacitive EMI filters.

The high level flow diagram of FIG. 3 will now be used to summarize methods according to embodiments of the present technology, which are for use with an ICD system that includes at least one defibrillation charge capacitor (e.g., C_(charge)) coupled between first and second voltage rails (e.g., 112 and 114), and also includes first, second, and third electrodes (e.g., 116 a, 116 b, and 116 c).

Referring to FIG. 3, step 302 involves providing a first filter coupled between the first and second electrodes, a second filter coupled between the second and third electrodes, and a third filter coupled between the first and third electrodes. The first filter coupled between the first and second electrodes, the second filter coupled between the second and third electrodes, and the third filter coupled between the first and third electrodes, provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock.

In accordance with certain embodiments, the first filter, which is coupled between the first and second electrodes, includes a first capacitor having a first terminal coupled to the first electrode and a second terminal coupled to the second electrode, the first capacitor having a first capacitance; the second filter, which is coupled between the second and third electrodes, includes a second capacitor having a first terminal coupled to the second electrode and a second terminal coupled to the third electrode, the second capacitor having a second capacitance; and the third filter, which is coupled between the first and third electrodes, includes a third capacitor having a first terminal coupled to the first electrode and a second terminal coupled to the third electrode, the third capacitor having a third capacitance. In accordance with certain embodiments, the first, second and third capacitances are substantially equal to one another to thereby provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock.

Still referring to FIG. 3, step 304 involves causing a high voltage potential to be stored on the at least one defibrillation charge capacitor coupled between the first voltage rail and the second voltage rail. Step 304 can be performed using a charge circuit (e.g., 108) that is controlled by a controller (e.g., 120).

Step 306 involves connecting a first subset of the first, second, and third electrodes to the first voltage rail, and a second subset of the first, second, and third electrodes to the second voltage rail, the first and second subsets differing from one another. For example, referring back to FIG. 2B, step 306 can involve connecting the electrode 116 a to the high voltage rail 112, and connecting the electrodes 116 b and 116 c to the low voltage rail 114.

Referring again to FIG. 3, step 308 involves discharging at least a portion of the high voltage potential stored on the at least one defibrillation charge capacitor, while the first subset of the first, second, and third electrodes are connected to the first voltage rail, and the second subset of the first, second, and third electrodes are connected to the second voltage rail. Referring briefly back to FIG. 2B, such discharging can begin by closing the switches Sw1, Sw5, and Sw6. One or more additional switches (not shown) can also be included and used to control when discharge of the at least one defibrillation charge capacitor occurs.

Referring again to FIG. 3, after the discharging of a portion of the high voltage potential stored on the at least one defibrillation charge capacitor at step 308, step 310 involves connecting the first subset of the first, second, and third electrodes to the second voltage rail, and the second subset of the first, second, and third electrodes to the first voltage rail. For example, referring back to FIG. 2B, step 310 can involve connecting the electrode 116 a to the low voltage rail 114, and connecting the electrodes 116 b and 116 c to the high voltage rail 112.

Referring again to FIG. 3, step 312 involves, discharging a further portion of the high voltage potential stored on the at least one defibrillation charge capacitor, while the first subset of the first, second, and third electrodes are connected to the second voltage rail, and the second subset of the first, second, and third electrodes are connected to the first voltage rail.

Steps 306 and 308 cause a first portion of a biphasic defibrillation shock to be delivered, and steps 310 and 312 cause a second portion of the biphasic defibrillation chock to be delivered.

In parallel with one or more of steps 304 through 312, a method can also include, at step 314, shunting EMI signals using the first filter coupled between the first and second electrodes, the second filter coupled between the second and third electrodes, and the third filter coupled between the first and third electrodes, when such EMI signals are present.

Further details of the methods summarized with reference to the high level flow diagram of FIG. 3 can be appreciated from the above discussion of FIGS. 1A through 2C.

For completeness, additional details of an exemplary cardiac stimulation device within which embodiments of the present technology can be implemented will now be describe with reference to FIGS. 4A and 4B. FIG. 4A illustrates an exemplary cardiac stimulation device, which is a dual-chamber stimulation device 402 capable of treating both fast and slow arrhythmias with stimulation therapy, including cardioversion, defibrillation, and pacing stimulation, including multi-site left ventricular (MSLV) pacing. This cardiac stimulation device 402 can be, or be part of, any one of the ICD systems described above with reference to FIGS. 1A-2C.

To provide atrial chamber pacing stimulation and sensing, cardiac stimulation device 402 is shown in electrical communication with a heart 413 by way of a right atrial (LA) lead 420 having an atrial tip electrode 422 and an atrial ring electrode 423 implanted in the atrial appendage. Cardiac stimulation device 402 is also in electrical communication with the heart by way of a right ventricular (RV) lead 430 having, in this embodiment, a ventricular tip electrode 432, a RV ring electrode 434, a RV coil electrode 436, and a superior vena cava (SVC) coil electrode 438. Typically, the RV lead 430 is transvenously inserted into the heart so as to place the RV coil electrode 436 in the RV apex, and the SVC coil electrode 438 in the superior vena cava. Accordingly, the RV lead is capable of receiving cardiac signals, and delivering stimulation in the form of pacing and shock therapy to the right ventricle (also referred to as the RV chamber).

To sense left atrial and ventricular cardiac signals and to provide left chamber pacing therapy, cardiac stimulation device 402 is coupled to a multi-pole LV lead 424 designed for placement in the “CS region” via the CS os for positioning a distal electrode adjacent to the left ventricle and/or additional electrode(s) adjacent to the left atrium (also referred to as the LA chamber). As used herein, the phrase “CS region” refers to the venous vasculature of the left ventricle, including any portion of the CS, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the CS. Accordingly, an exemplary LV lead 424 is designed to receive atrial and ventricular cardiac signals and to deliver left ventricular pacing therapy using a set of four LV electrodes 426 ₁, 426 ₂, 426 ₃, and 426 ₄ (thereby providing a quadra-pole lead), left atrial pacing therapy using at least a LA ring electrode 424, and shocking therapy using at least a LA coil electrode 428. In certain embodiments, the LV lead 424 includes the LV electrodes 426 ₁, 426 ₂, 426 ₃, and 426 ₄, but does not include the LA electrodes. Such a lead can be, e.g., the Quartet™ left ventricular pacing lead available from Abbott Laboratories (headquartered in Lake Bluff, Ill.), which includes four pacing electrodes on the left ventricular lead—enabling up to 10 pacing configurations.

The LV electrode 426 ₁ is shown as being the most “distal” LV electrode (with relation to how far the electrode is from where the LV lead 424 connects to the cardiac stimulation device 402). The LV electrode 426 ₄ is shown as being the most “proximal” LV electrode. The LV electrodes 426 ₂ and 426 ₃ are shown as being “middle” LV electrodes, between the distal and proximal LV electrodes 426 ₁ and 426 ₄. Accordingly, so as to more aptly describe their relative locations, the four LV electrodes 426 ₁, 426 ₂, 426 ₃, and 426 ₄ can be referred to respectively as electrodes D1, M2, M3 and P4 (where “D” stands for “distal”, “M” stands for “middle”, and “P” stands from “proximal”, and the numbers are arranged from most distal to most proximal).

It is also possible that more or fewer LV electrodes are provided. However, for much of the remaining discussion, it will be assumed that the multi-pole LV lead 424 includes the four LV electrodes 426 ₁, 426 ₂, 426 ₃, and 426 ₄ (i.e., LV electrodes D1, M2, M3 and P4, respectively).

The four LV electrodes can be used to provide various different pacing vectors and sensing vectors. Some of the vectors are intraventricular LV vectors (vectors between two LV electrodes); whereas others are interventricular vectors (e.g., vectors between a LV electrode and the RV coil 436). Below is a list of exemplary vectors that can be used for pacing and/or sensing using the LV electrodes D1, M2, M3 and P4 with and without the RV coil 436. In the following list, the first electrode in each row (i.e., the electrode to the left of the arrow) is assumed to be connected as the cathode, and the second electrode in each row (i.e., the electrode to the right of the arrow) is assumed to be connected as the anode, but that need not be the case, especially where neither electrode is a coil.

D1→RV coil

M2→RV coil

M3→RV coil

P4→RV coil

D1→M2

D1→P4

M2→P4

M3→M2

M3→P4

P4→M2

Although only three leads are shown in FIG. 4A, it should also be understood that additional leads (with one or more pacing, sensing and/or shocking electrodes) might be used and/or additional electrodes might be provided on the leads already shown, such as additional electrodes on the RV or LV lead. It is also possible that less than three leads be used.

A simplified block diagram of internal components of the cardiac stimulation device 402 is shown in FIG. 4B. While a particular cardiac stimulation device is shown, this is for illustration purposes only, and one of skill in the art could readily duplicate, eliminate or disable the appropriate circuitry in any desired combination to provide a device capable of treating the appropriate chamber(s) with cardioversion, defibrillation and pacing stimulation. The housing 440 for cardiac stimulation device 402, shown schematically in FIG. 4B, is often referred to as the “can”, “case” or “case electrode” and may be programmably selected to act as the return electrode for all “unipolar” modes. The housing 440 may further be used as a return electrode alone or in combination with one or more of the coil electrodes, 428, 436 and 438, for shocking purposes. The housing 440 further includes a connector (not shown) having a plurality of terminals, 442, 443, 444 ₁-444 ₄, 446, 448, 452, 454, 456 and 458 (shown schematically and, for convenience, the names of the electrodes to which they are connected are shown next to the terminals). As such, to achieve RA sensing and pacing, the connector includes at least a RA tip terminal (AR TIP) 442 adapted for connection to the atrial tip electrode 422 and a RA ring (AR RING) electrode 443 adapted for connection to RA ring electrode 423. To achieve left chamber sensing, pacing and shocking, the connector includes a LV tip terminal 444 ₁ adapted for connection to the D1 electrode and additional LV electrode terminals 444 ₂, 444 ₃ and 444 ₄ terminals adapted for connection to the M2, M3 and P4 electrodes of the quadra-pole LV lead.

The connector also includes a LA ring terminal (A_(L) RING) 446 and a LA shocking terminal (A_(L) COIL) 448, which are adapted for connection to the LA ring electrode 423 and the LA coil (A_(L) COIL) electrode 428, respectively. To support right chamber sensing, pacing and shocking, the connector further includes a RV tip terminal (V_(R) TIP) 442, a RV ring terminal (V_(R) RING) 443, a RV shocking terminal (V_(R) COIL) 456, and an SVC shocking terminal (SVC COIL) 458, which are adapted for connection to the RV tip electrode 432, RV ring electrode 434, the RV coil electrode 436, and the SVC coil electrode 438, respectively.

At the core of cardiac stimulation device 402 is a programmable microcontroller 460, which controls the various modes of stimulation therapy. As is well known in the art, the microcontroller 460 (also referred to herein as a control unit or controller) typically includes a microprocessor, or equivalent control circuitry, designed specifically for controlling the delivery of stimulation therapy and may further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. Typically, the microcontroller 460 includes the ability to process or monitor input signals (data) as controlled by a program code stored in a designated block of memory. The details of the design and operation of the microcontroller 460 are not critical to the technology. Rather, any suitable microcontroller 460 may be used that carries out the functions described herein. The use of microprocessor-based control circuits for performing timing and data analysis functions are well known in the art.

As shown in FIG. 4B, an atrial pulse generator 470 and a ventricular pulse generator 472 generate pacing stimulation pulses for delivery by the RA lead 420, the RV lead 430, and/or the LV lead 424 via an electrode configuration switching circuitry 444. It is understood that in order to provide stimulation therapy in each of the four chambers of the heart, the atrial and ventricular pulse generators, 470 and 472, may include dedicated, independent pulse generators, multiplexed pulse generators or shared pulse generators. The pulse generators, 470 and 472, are controlled by the microcontroller 460 via appropriate control signals, 486 and 488, respectively, to trigger or inhibit the stimulation pulses.

The microcontroller 460 includes timing control circuitry 461 to control the timing of the stimulation pulses, including, but not limited to, pacing rate, atrio-ventricular (AV) delay, interatrial conduction (AA) delay, interventricular conduction (W) delay and/or intraventricular delay (e.g., LV1-LV2 delay). The timing control circuitry 461 can also keep track of the timing of refractory periods, blanking intervals, noise detection windows, evoked response detection windows, alert intervals, marker channel timing, etc., which is well known in the art.

The microcontroller 460 further includes an arrhythmia detector 462. The detector 462 can be utilized by the stimulation device 402 for determining desirable times to administer various therapies. The detector 462 may be implemented in hardware as part of the microcontroller 460, or as software/firmware instructions programmed into the device and executed on the microcontroller 460 during certain modes of operation.

The microcontroller 460 further includes a capture detection module 463 and a morphology detection module 464. The aforementioned components may be implemented in hardware as part of the microcontroller 460, or as software/firmware instructions programmed into the device and executed on the microcontroller 460 during certain modes of operation. The microcontroller 460 can be used to implement the controllers (e.g. 120) discussed above with reference to FIGS. 1A through 3.

Additional components of the microcontroller include a MSLV controller 465 to control the actual delivery of MSLV pacing and a CRT controller 466 to control CRT, which can be performed in conjunction with MSLV pacing.

Depending upon the implementation, the various components of the microcontroller may be implemented as separate software modules or the modules may be combined to permit a single module to perform multiple functions. For example, the MSLV controller and the CRT controller 466 can be combined. In addition, although shown as being components of the microcontroller, some or all of these components may be implemented separately from the microcontroller, using application specific integrated circuits (ASICs) or the like.

Switching circuitry 444 includes a plurality of switches for connecting the desired electrodes to the appropriate I/O circuits, thereby providing complete electrode programmability. Accordingly, the switching circuitry 444, in response to a control signal 480 from the microcontroller 460, determines the polarity of the stimulation pulses (e.g., unipolar, bipolar, combipolar, etc.) by selectively closing the appropriate combination of switches (not shown) as is known in the art. The switching circuitry 444 also switches among the various LV electrodes. The switching circuitry 444 can include the switches Sw1 through Sw6 shown in and discussed above with references to FIGS. 1A through 3.

Atrial sensing circuits 482 and ventricular sensing circuits 484 may also be selectively coupled to the RA lead 420, LV lead 424, and the RV lead 430, through the switching circuitry 444 for detecting the presence of cardiac activity in each of the four chambers of the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR. SENSE) sensing circuits, 482 and 484, may include dedicated sense amplifiers, multiplexed amplifiers or shared amplifiers. The switching circuitry 444 determines the “sensing polarity” of the cardiac signal by selectively closing the appropriate switches, as is also known in the art. In this way, the clinician may program the sensing polarity independent of the stimulation polarity. Each sensing circuit, 482 and 484, preferably employs one or more low power, precision amplifiers with programmable gain and/or automatic gain control, bandpass filtering, and a threshold detection circuit, as known in the art, to selectively sense the cardiac signal of interest. The automatic gain control enables cardiac stimulation device 402 to deal effectively with the difficult problem of sensing the low amplitude signal characteristics of atrial or ventricular fibrillation. The outputs of the atrial and ventricular sensing circuits, 482 and 484, are connected to the microcontroller 460 which, in turn, are able to trigger or inhibit the atrial and ventricular pulse generators, 440 and 442, respectively, in a demand fashion in response to the absence or presence of cardiac activity in the appropriate chambers of the heart.

For arrhythmia detection, cardiac stimulation device 402 utilizes the atrial and ventricular sensing circuits, 482 and 484, to sense cardiac signals to determine whether a rhythm is physiologic or pathologic. As used in this section “sensing” is reserved for the noting of an electrical signal, and “detection” is the processing of these sensed signals and noting the presence of an arrhythmia, an evoked response, an intrinsic event, or some other event being monitored for. The timing intervals between sensed events (e.g., AS, VS, and depolarization signals associated with fibrillation which are sometimes referred to as “F-waves” or “Fib-waves”) can be classified by the microcontroller 460 by comparing them to a predefined rate zone limit (i.e., bradycardia, normal, atrial tachycardia, atrial fibrillation, low rate VT, high rate VT, and fibrillation rate zones) and various other characteristics (e.g., sudden onset, stability, physiologic sensors, and morphology, etc.) in order to determine the type of remedial therapy that is needed (e.g., bradycardia pacing, antitachycardia pacing, cardioversion shocks or defibrillation shocks). The arrhythmia detector 462, mentioned above, can be used to detect and characterize such arrhythmias.

Cardiac signals are also applied to the inputs of an analog-to-digital (A/D) data acquisition system 490. The data acquisition system 490 is configured to acquire intracardiac electrogram signals, convert the raw analog data into a digital signal, and store the digital signals for later processing and/or telemetric transmission to an external programmer 404 or a bedside monitor or personal advisory module (PAM) 405. The data acquisition system 490 is coupled to the RA lead 420, the LV lead 424, and the RV lead 430 through the switching circuitry 444 to sample cardiac signals across any pair of desired electrodes. The microcontroller 460 is further coupled to a memory 494 by a suitable data/address bus 496, wherein the programmable operating parameters used by the microcontroller 460 are stored and modified, as required, in order to customize the operation of cardiac stimulation device 402 to suit the needs of a particular patient. Such operating parameters define, for example, the amplitude or magnitude, pulse duration, electrode polarity, for both pacing pulses and impedance detection pulses as well as pacing rate, sensitivity, arrhythmia detection criteria, and the amplitude, waveshape and vector of each pacing and shocking pulse to be delivered to the patient's heart within each respective tier of therapy. Other pacing parameters include base rate, rest rate and circadian base rate.

Advantageously, the operating parameters of the implantable cardiac stimulation device 402 may be non-invasively programmed into the memory 494 through a telemetry circuit 401 in telemetric communication with an external device 404 or bedside monitor 405, such as a programmer, transtelephonic transceiver or a diagnostic system analyzer. The telemetry circuit 401 is activated by the microcontroller by a control signal 406. The telemetry circuit 401 advantageously allows intracardiac electrograms and status information relating to the operation of cardiac stimulation device 402 (as contained in the microcontroller 460 or memory 494) to be sent to the external device 405 through an established communication link 403. An internal warning device 421 may be provided for generating perceptible warning signals to the patient via vibration, voltage or other methods.

Cardiac stimulation device 402 further includes an accelerometer or other physiologic sensor 408, commonly referred to as a “rate-responsive” sensor because it is typically used to adjust pacing stimulation rate according to the exercise state of the patient. However, the physiological sensor 408 may further be used to detect changes in cardiac output, changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states) and to detect arousal from sleep. Accordingly, the microcontroller 460 can respond by adjusting the various pacing parameters (such as rate, AV delay, W delay, etc.) at which the atrial and ventricular pulse generators, 440 and 442, generate stimulation pulses. While shown as being included within cardiac stimulation device 402, it is to be understood that the physiologic sensor 408 may also be external to cardiac stimulation device 402, yet still be implanted within or carried by the patient. A common type of rate responsive sensor is an activity sensor incorporating an accelerometer or a piezoelectric crystal, which is mounted within the housing 440 of cardiac stimulation device 402. Other types of physiologic sensors are also known, for example, sensors that sense the oxygen content of blood, respiration rate and/or minute ventilation, pH of blood, ventricular gradient, stroke volume, cardiac output, contractility, etc.

The cardiac stimulation device additionally includes a battery 410, which provides operating power to all of the circuits shown in FIG. 4B. The battery 410 may vary depending on the capabilities of cardiac stimulation device 402. If the system only provides low voltage therapy, a lithium iodine or lithium copper fluoride cell typically may be utilized. For cardiac stimulation device 402, which employs shocking therapy, the battery 410 should be capable of operating at low current drains for long periods, and then be capable of providing high-current pulses (for capacitor charging) when the patient requires a shock pulse. The battery 410 should also have a predictable discharge characteristic so that elective replacement time can be detected. Accordingly, appropriate batteries are employed.

As further shown in FIG. 4B, cardiac stimulation device 402 is shown as having an impedance measurement circuit 412, which is enabled by the microcontroller 460 via a control signal 414. Uses for an impedance measurement circuit include, but are not limited to, lead impedance surveillance during the acute and chronic phases for proper lead positioning or dislodgement; detecting operable electrodes and automatically switching to an operable pair if dislodgement occurs; measuring respiration or minute ventilation; measuring thoracic impedance for determining shock thresholds; detecting when the device has been implanted; measuring respiration; and detecting the opening of heart valves, etc. The impedance measurement circuit 412 is advantageously coupled to the switching circuitry 444 so that any desired electrode may be used. The impedance measurement circuit 412 is an example of the impedance measurement circuit 504 discussed above with reference to FIG. 5.

In the case where cardiac stimulation device 402 is intended to operate as an ICD system, it detects the occurrence of an arrhythmia, and automatically applies an appropriate electrical shock therapy to the heart aimed at terminating the detected arrhythmia. To this end, the microcontroller 460 further controls a shocking circuit 473 by way of a control signal 449. The shocking circuit 473 generates shocking pulses of low (up to 0.1 joules), moderate (0.1-10 joules) or high energy (11 to 40 joules or more), as controlled by the microcontroller 460. Such shocking pulses are applied to the heart of the patient through at least two shocking electrodes, and as shown in this embodiment, selected from the LA coil electrode 428, the RV coil electrode 436, and/or the SVC coil electrode 438. The housing 440 may act as an active electrode in combination with the RV electrode 436, or as part of a split electrical vector using the SVC coil electrode 438 or the LA coil electrode 428 (i.e., using the RV electrode as a common electrode). Cardioversion shocks are generally considered to be of low to moderate energy level (so as to minimize pain felt by the patient), and/or synchronized with a R-wave and/or pertaining to the treatment of tachycardia. Defibrillation shocks are generally of moderate to high energy level (i.e., corresponding to thresholds in the range of 4-40 joules), delivered asynchronously (since R-waves may be too disorganized), and pertaining exclusively to the treatment of fibrillation. Accordingly, the microcontroller 460 is capable of controlling the synchronous or asynchronous delivery of the shocking pulses. The shocking circuit 473 can include, e.g., the charge circuit 108 and the charge capacitor(s) C_(charge) discussed above, but is not limited thereto.

The above described implantable device 402 was described as an exemplary cardiac stimulation device. One or ordinary skill in the art would understand that embodiments of the present technology can be used with alternative types of implantable devices. Accordingly, embodiments of the present technology should not be limited to use only with the above described device.

The terms “couple,” “coupled,” and “coupling,” and the like, as referred to herein, can refer to electrical components that are directly electrically connected to one another, or that are electrically connected to one another with one or more intermediate electrical component therebetween. For example, an electrode being coupled to a voltage rail can refer to the electrode being directly electrically connected to the voltage rail (e.g., by a wire and/or a closed switch), or there can be a sense resistor, or the like, also included in the electrical pathway between the electrode and the voltage rail. Conversely, if a switch between an electrode and a voltage rail were open, or there were some other open circuit between the switch and the electrode, then the electrode and the voltage rail would not be coupled to one another. In other words, for purposes of this document, a connection may be a direct connection or an indirect connection (e.g., via one or more other parts). In some cases, when an element is referred to as being connected or coupled to another element, the element may be directly connected to the other element or indirectly connected to the other element via intervening elements. When an element is referred to as being directly connected to another element, then there are no intervening elements between the element and the other element. Two devices are “in communication” if they are directly or indirectly connected so that they can communicate electronic signals between them.

The disclosure has been described in conjunction with various embodiments. However, other variations and modifications to the disclosed embodiments can be understood and effected from a study of the drawings, the disclosure, and the appended claims, and such variations and modifications are to be interpreted as being encompassed by the appended claims.

In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate, preclude or suggest that a combination of these measures cannot be used to advantage.

It is understood that the present subject matter may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this subject matter will be thorough and complete and will fully convey the disclosure to those skilled in the art. Indeed, the subject matter is intended to cover alternatives, modifications and equivalents of these embodiments, which are included within the scope and spirit of the subject matter as defined by the appended claims. Furthermore, in the above detailed description of the present subject matter, numerous specific details are set forth in order to provide a thorough understanding of the present subject matter. However, it will be clear to those of ordinary skill in the art that the present subject matter may be practiced without such specific details.

Aspects of the present disclosure are described herein with reference to flow diagrams and/or block diagrams of methods and apparatuses (systems) according to embodiments of the disclosure. It will be understood that at least some of the blocks of a flow diagram (e.g., in FIG. 3) can be implemented by computer program instructions. These computer program instructions may be provided to one or more processors of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor(s) of the computer or other programmable instruction execution apparatus, create a mechanism for implementing the functions/acts specified in the flow diagram and/or block diagram block or blocks. The computer-readable non-transitory media includes all types of computer readable media, including magnetic storage media, optical storage media, and solid state storage media and specifically excludes signals. It should be understood that the software can be installed in and sold with the device. Alternatively the software can be obtained and loaded into the device, including obtaining the software via a disc medium or from any manner of network or distribution system, including, for example, from a server owned by the software creator or from a server not owned but used by the software creator. The software can be stored on a server for distribution over the Internet, for example. Computer-readable storage media (medium) exclude (excludes) propagated signals per se, can be accessed by a computer and/or processor(s), and include volatile and non-volatile internal and/or external media that is removable and/or non-removable. For the computer, the various types of storage media accommodate the storage of data in any suitable digital format. It should be appreciated by those skilled in the art that other types of computer readable medium can be employed such as zip drives, solid state drives, magnetic tape, flash memory cards, flash drives, cartridges, and the like, for storing computer executable instructions for performing the novel methods (acts) of the disclosed architecture.

For purposes of this document, it should be noted that the dimensions of the various features depicted in the figures may not necessarily be drawn to scale.

For purposes of this document, reference in the specification to “an embodiment,” “one embodiment,” “some embodiments,” or “another embodiment” may be used to describe different embodiments or the same embodiment.

For purposes of this document, the term “based on” may be read as “based at least in part on.”

For purposes of this document, without additional context, use of numerical terms such as a “first” object, a “second” object, and a “third” object may not imply an ordering of objects, but may instead be used for identification purposes to identify different objects. Similarly, a “first” user, a “second” user, and a “third” user may not imply an ordering of users, but may instead be used for identification purposes to identify different users.

For purposes of this document, the term “subset” of objects may refer to a “subset” of one or more of the objects, unless stated otherwise.

The foregoing detailed description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the subject matter claimed herein to the precise form(s) disclosed. Many modifications and variations are possible in light of the above teachings. The described embodiments were chosen in order to best explain the principles of the disclosed technology and its practical application to thereby enable others skilled in the art to best utilize the technology in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope be defined by the claims appended hereto.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the embodiments of the present technology. While the technology has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the technology. 

What is claimed is:
 1. An implantable cardioverter device (ICD) system configured to be implanted within a patient and capable of delivering a multi-vector defibrillation shock, the ICD comprising: at least one defibrillation charge capacitor coupled between a first voltage rail and a second voltage rail; a charge circuit configured to selectively cause a high voltage potential to be stored on the at least one defibrillation charge capacitor; first, second, and third electrodes that can be used to selectively deliver at least a portion of the high voltage potential, stored on the at least one defibrillation charge capacitor, to patient tissue that is in contact with at least one of the first, second, and third electrodes; a plurality of switches; a controller configured to control the plurality of switches to selectively connect a first subset of the first, second, and third electrodes to the first voltage rail, and selectively connect a second subset of the first, second, and third electrodes to the second voltage rail, such that there is no overlap between electrodes within the first and second subsets; a first filter coupled between the first and second electrodes, and a second filter coupled between the second and third electrodes, the first and second filters configured to shunt electromagnetic interference (EMI) signals; and a third filter coupled between the first and third electrodes and configured to provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock.
 2. The ICD system of claim 1, wherein in order to deliver a biphasic multi-vector defibrillation shock, while the high voltage potential stored on the at that least one defibrillation charge capacitor is being discharged, the controller controls the plurality of switches to: connect the first subset of the first, second, and third electrodes to the first voltage rail, and connect the second subset of the first, second, and third electrodes to the second voltage rail, for a first period of time during which the high voltage potential is being discharged; and connect the first subset of the first, second, and third electrodes to the second voltage rail, and connect the second subset of the first, second, and third electrodes to the first voltage rail, for a second period of time during which the high voltage potential is being discharged.
 3. The ICD system of claim 1, wherein: the first electrode comprises a right ventricular (RV) electrode; the second electrode comprises a case electrode; and the third electrode comprises a superior vena cava (SVC) electrode.
 4. The ICD system of claim 1, wherein the switches are controlled to selectively connect: two of the first, second, and third electrodes to the first voltage rail and a remaining one of the first, second, and third electrodes to the second voltage rail; or one of the first, second, and third electrodes to the first voltage rail and a remaining two of the first, second, and third electrodes to the second voltage rail.
 5. The ICD system of claim 1, wherein: the first filter, which is coupled between the first and second electrodes, comprises a first capacitor having a first terminal coupled to the first electrode and a second terminal coupled to the second electrode, the first capacitor having a first capacitance; the second filter, which is coupled between the second and third electrodes, comprises a second capacitor having a first terminal coupled to the second electrode and a second terminal coupled to the third electrode, the second capacitor having a second capacitance; the third filter, which is coupled between the first and third electrodes, comprises a third capacitor having a first terminal coupled to the first electrode and a second terminal coupled to the third electrode, the third capacitor having a third capacitance; the first, second and third capacitances are substantially equal to one another to thereby provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock.
 6. The ICD system of claim 5, wherein one or more of the first, second, and third capacitors comprise feedthrough capacitor(s) that is/are located within a header of the ICD system.
 7. The ICD system of claim 5, wherein one or more of the first, second, and third capacitors is/are located on or within a substrate that is within a housing of the ICD system.
 8. The ICD system of claim 1, wherein the first, second, and third electrodes, the first and second filters, and the plurality of switches, are collectively configured to provide a plurality of H-bridge circuits, wherein inclusion of the third filter causes the H-bridge circuits to be symmetrical, and wherein at least one of the H-bridge circuits would be asymmetrical if the third filter were not present.
 9. The ICD system of claim 1, wherein the switches comprise silicon-controlled rectifiers.
 10. The ICD system of claim 1, wherein the filters provide for compatible with magnetic resonance imaging (MRI) systems.
 11. A method for use with an implantable cardioverter device (ICD) system that includes at least one defibrillation charge capacitor coupled between first and second voltage rails, and also includes first, second, and third electrodes, the method comprising: providing a first filter coupled between the first and second electrodes, a second filter coupled between the second and third electrodes, and a third filter coupled between the first and third electrodes; causing a high voltage potential to be stored on the at least one defibrillation charge capacitor coupled between the first voltage rail and the second voltage rail; connecting a first subset of the first, second, and third electrodes to the first voltage rail, and a second subset of the first, second, and third electrodes to the second voltage rail, the first and second subsets differing from one another; and discharging at least a portion of the high voltage potential stored on the at least one defibrillation charge capacitor, while the first subset of the first, second, and third electrodes are connected to the first voltage rail, and the second subset of the first, second, and third electrodes are connected to the second voltage rail.
 12. The method of claim 11, further comprising: shunting electromagnetic interference (EMI) signals using the first filter coupled between the first and second electrodes, the second filter coupled between the second and third electrodes, and the third filter coupled between the first and third electrodes.
 13. The method of claim 11, further comprising, after the discharging the at least a portion of the high voltage potential stored on the at least one defibrillation charge capacitor: connecting the first subset of the first, second, and third electrodes to the second voltage rail, and the second subset of the first, second, and third electrodes to the first voltage rail; and discharging a further portion of the high voltage potential stored on the at least one defibrillation charge capacitor, while the first subset of the first, second, and third electrodes are connected to the second voltage rail, and the second subset of the first, second, and third electrodes are connected to the first voltage rail.
 14. The method of claim 11, wherein the first filter coupled between the first and second electrodes, the second filter coupled between the second and third electrodes, and the third filter coupled between the first and third electrodes, provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock.
 15. The method of claim 11, wherein: the first filter, which is coupled between the first and second electrodes, comprises a first capacitor having a first terminal coupled to the first electrode and a second terminal coupled to the second electrode, the first capacitor having a first capacitance; the second filter, which is coupled between the second and third electrodes, comprises a second capacitor having a first terminal coupled to the second electrode and a second terminal coupled to the third electrode, the second capacitor having a second capacitance; the third filter, which is coupled between the first and third electrodes, comprises a third capacitor having a first terminal coupled to the first electrode and a second terminal coupled to the third electrode, the third capacitor having a third capacitance; and the first, second and third capacitances are substantially equal to one another to thereby provide for electrical symmetry when the first, second, and third electrodes are used to deliver a multi-vector defibrillation shock.
 16. An implantable cardioverter device (ICD) system configured to be implanted within a patient and capable of delivering a multi-vector defibrillation shock, the ICD comprising: at least one defibrillation charge capacitor coupled between a first voltage rail and a second voltage rail; a charge circuit configured to selectively cause a high voltage potential to be stored on the at least one defibrillation charge capacitor; first, second, and third electrodes that can be used to selectively deliver at least a portion of the high voltage potential, stored on the at least one defibrillation charge capacitor, to patient tissue that is in contact with at least one of the first, second, and third electrodes; a plurality of switches; a controller configured to control the plurality of switches to selectively connect a first subset of the first, second, and third electrodes to the first voltage rail, and selectively connect a second subset of the first, second, and third electrodes to the second voltage rail, such that there is no overlap between electrodes within the first and second subsets; and a first capacitor coupled between the first and second electrodes, a second capacitor coupled between the second and third electrodes, and a third capacitor coupled between the first and third electrodes.
 17. The ICD system of claim 16, wherein: capacitances of the first, second, and third capacitors are substantially equal to one another.
 18. The ICD system of claim 16, wherein: one or more of the first, second, and third capacitors is/are feedthrough capacitor(s) located within a header of the ICD system; or one or more of the first, second, and third capacitors is/are located on or within a substrate that is within a housing of the ICD system.
 19. The ICD system of claim 16, wherein: the switches comprise silicon-controlled rectifiers.
 20. The ICD system of claim 16, wherein: the first electrode comprises a right ventricular (RV) electrode; the second electrode comprises a case electrode; and the third electrode comprises a superior vena cava (SVC) electrode. 